Variations in cell length and frequency of anticlinal division in the vascular cambium throughout a white spruce tree

摘要

In the early growth of the stem, branches, and roots, the vascular elements are relatively short and the frequency of anticlinal division involved in cambial cell multiplication is high. As growth sheaths are added in the stem, length of cell increases and rate of multiplicative division declines. A similar trend occurs upward through the lower quarter to half the height of the stem. In the root system, the later growth of vertical roots is characterized by shortness of cell and high frequency of anticlinal division, and conversely, that of horizontal roots by great length of cell and low rate of anticlinal division. Although a general negative relationship exists between rate of anticlinal division and cell length throughout much of the tree, these features sometimes vary independently, and length of cell seems to be more closely related to amount of yearly radial accretion. Through the middle to late growth of the stem a negative relationship obtains between length of cell and width of annual ring, cell length maximating at a ring width of 1ndash;2ensp;mm. At this stage, frequency of division may fluctuate only narrowly over a considerable range of ring width. A continued decline in ring width to less than 0.5ensp;mm, such as may occur on senescence, is accompanied by decreased cell length and accelerated anticlinal division. Length of the cell plate in anticlinal division, relative to that of the dividing cell, is greater in the early growth of the stem and branches and throughout horizontal roots than elsewhere in the tree. Most of the anticlinal divisions are pseudotransverse. The proportion of lateral divisions ranges from about 1 in the late growth of stems to 11 in horizontal roots.